It's likely that the seal around the magnet was not good enough, and the magnet is corroding. Probably what you need is a new keypad- a very easy fix. In some cases I know Atomic has been able to send the keypad directly to the consumer, so long as they know the serial #- they need that to know which keypad to send. If you can be without the Cobalt for a short while you could send it back for a going-over. Which option you prefer might be dependent on where you are located. But it's a good bet the keypad is all you need.
I will PM you with cover removal instructions, you can check to see if you spot corrosion.
Ron